Instrument cluster lens assemblies are commonly used in vehicles to cover a group of gauges and indicators such as a fuel gauge, temperature indicator, speedometer, or tachometer. Some known instrument cluster lens assemblies have an injected molded lens that is connected to a retainer by fasteners such as screws or by ultrasonic or vibration welding.
One known type of instrument cluster lens assembly has a flat lens that is pressed against a curved surface of a retainer by ultrasonic welding apparatus and bonded to the perimeter of the retainer. However, both the retainer and the ultrasonic welding horn must be shaped to conform to the desired lens shape. Thus, each instrument cluster lens assembly must have a uniquely designed ultrasonic welding horn which greatly reduces manufacturing flexibility and increases production costs.
Moreover, ultrasonic and vibration welding require that the welding horn have direct physical contact with the lens, which produces unwanted scratching that leads to quality concerns and an increased number of parts that are rejected as scrap. In addition, ultrasonic and vibration welding require that the entire lens move relative to the retainer to create heat at a weld interface. As welds are initially created, they are also broken due to the relative movement. The scrubbing action between the parts leads to weld lines that have "hairs" along their outer edges. The hairs are visible through the lens and are aesthetically unattractive.
Further, ultrasonic and vibration welding require that the lens and retainer be produced with tighter tolerances because of the need for exact alignment between the mating surfaces of the parts, otherwise, frictional heat would not be generated. In addition, tighter tolerances are required to ensure that the lens and retainer are able to properly align with the shape of the welding horn.
Although laser welding is a known technique for joining two components together, laser welding has historically been used to join two components made from the same material. Accordingly, laser welding has not been successfully used to join a lens and retainer of an instrument cluster assembly because the lens and retainer are usually fabricated from dissimilar materials.